1. Field of the Invention
The field of the invention is inhalers for dry powder inhalants or drugs.
2. Description of the Prior Art
Beginning in the early 1970's, it was found that certain medicines could be administered in dry-powder form directly to the lungs by inhalation through the mouth or inspiration through the nose. This process allows the medicine to bypass the digestive system, and in some cases, allows smaller doses to be used to achieve the same desired results as orally ingested medicines. In other cases, it provides a delivery technique for medicines that display unacceptable side effects when taken by other methods.
Various devices or nebulizers that form inhalable mists of medicines are known in the art. They are divided between those that form mists of liquid medicines, those that form mists of powdered medicines, and those that may be used to form mists of both liquids and powders. The physical characteristics of powdered medicines, with particle sizes ranging from about 1 micron (0.001 mm) to about 100 microns, and more particularly from about 1 to about 5 microns, are significantly different from those of liquid medicines. There is little similarity between the engineering requirements and the physical designs of these two types of devices. Although some devices are intended to aerosolize both liquid and dry powder medicines, these devices would not appear to be highly efficient in operation.
Typical prior art devices for handling dry medicines are shown and described in U.S. Pat. Nos. 3,507,277; 3,518,992; 3,635,219; 3,831,606; 3,971,377; and 4,147,166. Several of these devices have been used, however, most of them have apparently not found wide acceptance. Most of these prior art devices use powdered medicine contained in a gelatin capsule with a separate dose contained in each capsule. These capsules are small and require significant manual dexterity to load and unload. A large portion of potential users of dry powdered medicines are found in the senior-citizen sector of the population and, unfortunately, this coincides with the major group of those inflicted with various forms of arthritis. With the minute size of the capsules and the requirements to load and unload them each time the nebulizer is used, they can be difficult to use.
Further, loading individual capsules with individual doses of powdered medicines can be time-consuming and thus makes the dosage in capsule a costly item. People who use a nebulizer during their daily routine are required to carry a large number of capsules which might leak thus lowering the effective dosage of the medicine.
Virtually all of these known devices involve the use of capsules that are pierced along their sides by needles or other sharp objects. Thereafter, the powdered medicine is slowly withdrawn from the capsules by either partial vacuum, caused by forced inspiration by the user, or by centrifugal force. Some of these devices require prolonged forced inspiration to extract the medicine. This requires the user to repeatedly inhale rather large volumes of air, each with a little dose of medicine, which can cause dizziness. In addition, all of the powder in the capsule may not be inhaled.
Water can pass through the walls of gelatin capsules. In high humidity areas, water vapor can penetrate the capsule and cake the medicine. If caked, it is extremely unlikely that all of the medicine would be inhaled from the capsule so that the dosage between capsules would vary, thus reducing the effect of the medicine.
Slow introduction of powdered medicine from the perforated capsule into the aerosolizing chamber, coupled with the airflow through the chamber, means that not all of the powder particles are present in the chamber at any one time. It has been found that self-scouring or inter-particle impact is an important feature in clearing the powdered medicine from the chamber for introduction into the lungs. Accordingly, dribbling the powdered medicine out of the capsule and into the chamber reduces the amount of self-scouring and allows cake buildup of the medicine in various parts of the chamber.
Another important factor is that it has not been realized that several important benefits are obtained if the delivery of a drug is relatively independent of the patient's inspiratory flow rate (i.e., how deeply the patent inhales) or coordination (i.e., the patient's timing of the inhalation). An inspiratory flow rate independent device can be used by patients with low inspiratory flow rates, such as children or patients experiencing aspiratory distress. Moreover, if the delivery of a drug is independent of the patient's inspiratory flow rate, the inhaled dosage will remain relatively consistent regardless of the patient's inhalation characteristics. Metered dose inhalers, typically using a propellant gas, require significant coordination for proper use. Actuation must occur during inspiration, or the majority of the drug will be deposited in the throat. It is now appreciated that a breath-actuated device will minimize the need for patient coordination.
Whether or not to allow the user to exhale into the device can be an important factor. The perforated capsules admit medicine very slowly into the inhalating airstream. In addition, many users are elderly persons or those who suffer from lung disease. These two factors may combine to render the user incapable of inhaling all of the medicine in one breath. Therefore, it is important to consider the possibility that the user will exhale into the device. Exhaling involves a high-humidity airstream. When it enters the device, it may cause some moisture condensation on the interior walls. In other cases, moisture-laden air may be blown into the aerosolizing chamber causing the powdered medicine to cake and fail to be extracted by later inhalations. Consequently, repeated exhaling into a device and its potential for caking of powdered medicine remains a significant disadvantage.
Moreover, the beneficial effects of reducing the size of large particles or agglomerated particles during use of the device have apparently not been appreciated previously. Large or agglomerated particles of medicine gather momentum during forced inhalation or inspiration and impact the soft, wet tissue surrounding the throat and larynx instead of remaining in the air flow for deposit in the lungs. When this occurs, much of the medicine apparently does not reach deep into the interior of the lungs and thus is not placed in a strategic location where it will be solvated for direct absorption through the areolar tissue into the blood stream. In more severe cases, such impact may cause coughing and thus could force large volumes of moisture-laden air, as well as finely dispersed saliva, to be reinjected into the device leading to caking of the medicine.
Accordingly, it is an object of the invention to provide an improved dry powder inhaler.